Parasitic control valve, elimination

For variable-speed pumps, such as steam turbine-driven pumps, control valves should not be used. The facility shown in Fig. 38.2 is a control scheme that is used not infrequently at older plants. It s a fine piece of technology, which has been lost with time. No control valve is used. The turbine speed is altered to directly maintain the vessel level. With the increasing use of variable-speed alternating-current motors, elimination of parasitic control valves should become more common. 

Pumps are driven by either fixed-speed or variable-speed motors. Variable-speed motors are becoming increasingly common. Flow can be controlled by varying the pump speed with the motor and thus eliminating parasitic energy losses across a flow control valve. However, because of the extra electronic components needed for a variable-speed AC motor, 95 percent of the motors we work with are fixed-speed alternating-current motors. I will only discuss fixed-speed, alternating-current (AC) motors in this chapter. 

In this section, we report on the combination of PDMS-based RF electronic devices and pneumatic valves to achieve a pneumatically-switched RF coplanar waveguide. PDMS has stable high frequency dielectric constant and low loss [21], while pneumatic valve technology offers a non-electronic form of control of RF devices eliminating electromagnetic interference and parasitic effects caused by bias lines. The outcomes present opportunities for pneumatically-switched addressable RF devices and elements. These can be utilized to control RF transmission in order to potentially activate or disable RF devices such as antenna and metamaterials [28]. 

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See also in sourсe #XX -- [ ]

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